Method and apparatus for measuring force particularly torque

ABSTRACT

A method and apparatus for measuring the force applied by a first member coupled to a second member by a connecting body, by: transmitting a cyclically-repeating energy wave through the connecting body from a first location thereon to a second location thereon; measuring the transit time of the cyclically-repeating energy wave from the first location to the second location; and utilizing the measured transit time to produce a measurement of the force. In the preferred described embodiment, the connecting body is a fastening plate which fastens a drive shaft to a driven shaft and measures the torque output of the drive shaft.

RELATED APPLICATIONS

This application is a National Phase Application of PCT PatentApplication No. PCT/IL2004/001190 having International Filing Date ofDec. 30, 2004, which claims the benefit of Israel Patent Application No.159651 filed on Dec. 30, 2003. The contents of the above Applicationsare all incorporated herein by reference.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for measuringforce, particularly torque. The invention is especially useful inmeasuring the output torque of a vehicle, and/or other forcesencountered in a motor vehicle. The invention is therefore describedbelow with respect to such applications, but it will be appreciated thatthe invention is capable of being used in many other applications aswell.

The instantaneous output torque of a vehicle engine can be used forcontrolling the fuel fed to the engine, and/or the ignition of the fuel,in order to increase the efficiency of the vehicle engine. It can alsobe used to provide an indication that an engine overhaul may be needed.Many torque measuring devices have been used for these purposes.However, efforts are continually being made to increase the precision ofthe torque measurement, to decrease the sensitivity of the torquemeasurement to rotational velocity or temperature variations, and/or toprovide a more simple and compact construction capable of convenientintroduction into existing vehicles and of withstanding the harshenvironmental conditions therein.

OBJECTS AND BRIEF SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to provide a method, and alsoapparatus, for measuring torque and other forces, having advantages inone or more of the above respects particularly when used in theabove-mentioned applications in motor vehicles.

According to one broad aspect of the present invention, there isprovided a method of measuring a force applied by a first member to asecond member via a connecting body, comprising: comprising:transmitting a cyclically-repeating acoustical wave through atransmission channel in said connecting body from a first locationthereon to a second location thereon; measuring the transit time of saidacoustical wave through said transmission channel from said firstlocation to said second location; and utilizing said measured transittime to produce a measurement of said force.

In the preferred embodiment of the invention described below, theconnecting body is a fastening plate which fastens the first member tothe second member, the two members being rotary members fastened forrotation together about a common axis by the fastening plate, such thatthe force measured is the torque applied by the first rotary member tothe second rotary member.

According to another aspect of the present invention, there is provideda method of measuring the torque applied by a drive shaft to a drivenshaft along a common axis of rotation, comprising: coupling the shaftstogether by fixing at least one torque sensor plate to one of the shaftsat a first fixation point eccentric with respect to the common axis ofrotation, and to the other one of the shafts at a second fixation pointspaced from the first fixation point; measuring the deformation of thetorque sensor plate in a section thereof between the first and secondfixation points; and utilizing the measured deformation to produce ameasurement of the torque; the second fixation point being spaced fromthe first fixation point along a tangential line substantiallyperpendicular to a radial line from the first fixation point to the axisof rotation, such that the deformed section of the torque sensor platebetween the first and second fixation points is expanded or contracted,depending on the direction of rotation of the drive shaft.

According to a further aspect of the present invention, there isprovided apparatus for measuring a force applied by a first member to asecond member via a connecting body, comprising: a transmitter at afirst location on the connecting body for transmitting acyclically-repeating acoustical wave through a transmission channel inthe connecting body to a second location thereon; a receiver at thesecond location on the connecting body for receiving thecyclically-repeating acoustical wave; and an electrical system formeasuring the transit time of the cyclically-repeating acoustical wavethrough the transmission channel from the first location to the secondlocation and for utilizing the measured transit time to produce ameasurement of the force.

Other aspects of the invention provide apparatus for measuring torque orother forces in accordance with the above method.

As will be described more particularly below, the method and apparatusincluding the foregoing features enable measuring torque with highprecision and with relative insensitivity to rotational velocity andtemperature variations. In addition, the method may be implemented inapparatus which is of a relatively simple, compact construction, andwhich is capable of convenient introduction into existing vehicles andof withstanding the harsh environmental conditions therein.

Particularly good results are obtainable when the measurement of thedeformation in the connecting member (e.g., the torque sensor plate) iseffected according to the high-precision measurement system described inU.S. Pat. No. 6,621,278, of Sep. 16, 2003, assigned to the assignee ofthe present application, although it will be appreciated that otherdeformation measuring systems could also be used, such as by the use ofconventional strain gauges.

Further features and advantages of the invention will be apparent fromthe description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is an exploded three-dimensional view illustrating a torquemeasuring device constructed in accordance with the present invention,but showing only one of the three torque sensor plates therein;

FIG. 2 is an end view diagrammatically illustrating the torque measuringdevice of FIG. 1 with the three torque sensor plates thereof;

FIG. 3 is an enlarged, fragmentary sectional view illustrating the onetorque sensor plate of FIG. 1 and the manner it is coupled to the driveand driven shafts as shown in FIG. 1;

FIG. 4 is an enlarged view of the torque sensor plate of FIGS. 1 and 3and its connection to the electrical system for measuring the torquesensed by the torque sensor plate;

FIG. 5 is a block diagram illustrating the electrical measuring systemof FIG. 4; and

FIG. 6 illustrates a modification in the torque sensor plate shown inFIG. 4.

It is to be understood that the foregoing drawings, and the descriptionbelow, are provided primarily for purposes of facilitating understandingthe conceptual aspects of the invention and various possible embodimentsthereof, including what is presently considered to be a preferredembodiment. In the interest of clarity and brevity, no attempt is madeto provide more details than necessary to enable one skilled in the art,using routine skill and design, to understand and practice the describedinvention. It is to be further understood that the embodiments describedare for purposes of example only, and that the invention is capable ofbeing embodied in other forms and applications than described herein.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIGS. 1-5 of the drawings illustrate a novel torque measuring method andapparatus in accordance with the present invention implemented in anautomotive vehicle for producing a continuous measurement of the enginetorque. In the illustrated implementation, the torque measurement iseffected in the coupling between the flywheel connected to the engineoutput shaft, and the clutch disc connected to the engine gearbox shaft.This connection is typically made by three fastening bolts securing theflywheel to the clutch disc at their outer peripheries. Thus, themechanical energy from the engine is transmitted via the flywheel andclutch disc by means of these three bolts. Each bolt is loaded with atotal shearing force F=M/R, wherein “M” is the force applied to thebolt, and “R” is the distance between the disc axis of rotation and thebolt axis. The engine torque is the total force (3F) applied to thethree bolts.

In the embodiment of the invention illustrated in FIGS. 1-5, the loadingof these bolts is sensed in order to provide a measurement of the outputtorque of the engine.

Thus, FIG. 1 illustrates the coupling between the flywheel 2 connectedto the engine via drive shaft 3, and the clutch disc 4 connected to theload via driven shaft 5 and the gearbox (not shown). This coupling iseffected by the three fastening bolts mentioned above, one of which isshown at 6. Each fastening bolt 6 passes through an opening 7 in theflywheel disc 2 and is threaded into a threaded member 9 fixed to theclutch disc 4.

In accordance with the present invention, a fastening plate, generallydesignated 10, serving as a torque sensor plate, is coupled by eachfastening bolt 6 to flywheel disc 2 and the clutch disc 4 in a manner tosense the torque transmitted via the respective bolt. While FIG. 1illustrates only one such torque sensor plate 10 for bolt 6, it will beappreciated that there are three such torque sensor plates, asschematically shown at 10 a, 10 b and 10 c in FIG. 2, each secured by afastening bolt 6 a, 6 b, 6 c, respectively.

Each torque sensor plate 10 is of a flat, elongated configuration bestseen in FIG. 4. It is widest at its central section and decreases inwidth towards its two end sections. Its central section is formed with acentral opening 11 for receiving its fastening bolt 6 which, asdescribed above, also secures the flywheel disc 2 to the clutch disc 4.Its two end sections are formed with openings 12, 13. Each of the latteropenings receives another fastening bolt 14, 15, which bolts passthrough aligned openings in the flywheel disc 2 alone. Bolts 14, 15receive locking rings 16, 17, and nuts 18, 19 (FIGS. 1 and 3) to securethe opposite ends of the torques sensor plate 10 to the flywheel disc 2.

It will thus be seen, as shown particularly in FIG. 3, each fastenerbolt 6, passing through the center of its respective torque sensor plate10, serves to fix the torque sensor plate to the clutch disc 4 at afirst fixation point eccentric with respect to the common axis ofrotation of the two discs defined by shafts 3 and 5. It will also beseen that the other two fastener bolts 14, 15, passing through the endopenings 12, 13 of the respective torque sensor plate 10, serve to fixthe torque sensor plate to the flywheel disc 2 at second and thirdfixation points, respectively, equally spaced on opposite sides of thefirst fixation point of fastener bolt 6. Thus, the torque transmitted byflywheel disc 2 to the clutch disc 4 will subject each torque sensorplate 10 to strains or deformations corresponding to the torquetransmitted, as will be described more particularly below.

FIG. 2 illustrates the assembly of FIG. 1 when all three torque sensorplates are applied for coupling the flywheel disc 2 to the clutch disc 4in the manner described above with respect to the single torque sensorplate 10 of FIG. 1. In FIG. 2, the three torque sensor plates, eachcorresponding to plate 10 in FIG. 1, are identified as 10 a, 10 b and 10c, respectively; and their three fastening bolts, corresponding to bolts6, 14 and 15 in FIG. 1, are identified as 6 a-6 c, 14 a-14 c and 15 a-15c, respectively.

As shown particularly in FIG. 2, each of the three torque sensor plates10 a, 10 b, 10 c is mounted such that the first fixation point effectedby the three bolts 6 a, 6 b, 6 c, is eccentric with respect to thecommon rotary axis RA of the two shafts 3, 5. In addition each of thesecond and third fixation points, effected by the bolts 14 a-14 c and 15a-15 c, respectively, is on a tangential line passing through therespective first fixation point of the respective bolts 6 a-6 c, i.e.,on a line which is substantially perpendicular to a radial line RL fromthe respective first fixation point to the rotary axis RA of the twoshafts. Thus, during the rotation of the shaft of the flywheel disc 2, aforce will be applied by each of the three bolts 6 a-6 c to the threetorque sensor plates 10 a-10 c in the tangential direction, as shown byarrows A-C, respectively, in FIG. 2. Such a tangential force applied byeach of the three bolts 6 a-6 c will produce a contraction of a sectionof the respective torque sensor plate 10 a-10 c between the firstfixation point (bolts 6 a-6 c) and the second fixation point (bolts 14a-14 c ), and an expansion of the section of the torque sensor plate onthe opposite side, i.e., between the first fixation point (bolts 6 a-6c) and the third fixation point (bolts 15 a-15 c ).

The contracted and expanded sections of each torque sensor plate 10 aremore particularly seen in FIG. 4. As shown, each torque sensor plate 10is formed with a slot formation, generally designated 20, to increasethe contraction and expansion of the sections of the torque sensor platebetween the above-described three fixation points. Slot formation 20includes a first pair of parallel slots 21, 22 between the centralopening 11 and one end opening 12, and a second pair of parallel slots23, 24 between the center opening 11 and the other end opening 13. Slots21, 22 thus define a first deformable section 25 between openings 11 and12; and slots 23, 24 define a second deformable section 26 betweenopenings 11 and 13. It will be seen that the two sections 25, 26 aredeformed in opposite senses during the rotation of the two discs 2, 4,according to the force applied to their respective fastener bolts 6;that is, when one of these sections is contracted, the other iselongated an equal amount.

Slot formation 20 formed in each torque sensor plate 10 includes twofurther pairs of parallel slots 31, 32 and 33, 34, respectively, located90° with respect to slot pairs 21, 22 and 23, 24. A deformable section35 is thus defined by slot pair 31, 32, and another deformable section36 is defined by slot pair 33, 34. However, whereas sections 25 and 26of the torque sensor plate are deformable by contraction or elongation,sections 35 and 36 are deformable by bending. The bending in sensorsections 35 and 36 thus increases the contraction or elongation insensor sections 25, 26.

The contraction or elongation in sensor sections 25, 26 is furtherincreased by the additional slots shown in FIG. 4, namely the outwardlyextending end slots 37-40 formed at the outer ends of the parallel slots21-24, respectively, and the connecting slots 41-44 interconnecting thetwo pairs of slots 21-24 with the two pairs of slots 31-34.

It will thus be seen that the contraction or elongation of sections 25and 26 of each torque sensor plate 10 will correspond to the force onthe respective center fastener bolt produced by the torque transmittedfrom the flywheel disc 2 to the clutch disc 4 via the respective torquesensor plate 10. The contraction or elongation of sensor sections 25, 26may be measured by conventional strain gauges. Particularly good resultsare obtainable, however, when such deformations are measured by theelectrical measuring system described in the above-cited U.S. Pat. No.6,621,278, which permits extremely high accuracy to be achieved evenwith relative small deformations.

Such an electrical measuring system is schematically indicated by box 50in FIG. 4, and is more particularly shown in FIG. 5. Broadly speaking,the deformation in each of the sections 25, 26 of the torque sensorplate 10 is measured by: transmitting a cyclically-repeating energy wavefrom one side of the respective section towards the other side;receiving the cyclically-repeating energy wave at the other side of therespective section; continuously changing the frequency of transmissionof the cyclically-repeating energy wave such that the number of wavesreceived is a whole integer; measuring the change in frequency; andutilizing the measured changes in frequency to produce a measurement ofthe deformations of the respective sensor sections 25, 26.

Such a measurement would thus be of the force on the fastener bolt 6 ofthe respective torque sensor plate produced by the engine torque. Thus,the total engine torque, i.e., the total torque transmitted between theflywheel disc 2 and the clutch disc 4, would be the summation of thetorques transmitted by the three torque sensor plates 10 a, 10 b and 10c coupling the two discs together via the three fastener bolts 6 a-6 c.

As shown in FIG. 4, each torque sensor plate 10 is provided with a firsttransmitter 51 at one side of its deformable section 25; a firstreceiver 52 at the opposite side of its deformable section 25; a secondtransmitter 53 at one side of its deformable section 26; and a secondreceive 54 at the opposite side of its deformable section 26. In thedescribed preferred embodiment, the two transmitters and receivers areboth of the acoustical type for transmitting and receivingcyclically-repeating acoustical waves.

The electrical measuring system shown within block 50 in FIG. 4, formeasuring the elongation and contraction of the sensor sections 25 and26 of the torque sensor plates 10 a-10 c, is more particularlyillustrated in FIG. 5. For the sake of simplicity, FIG. 5 illustratesonly the circuitry of the electrical system operative with transmitter51 and receiver 52 for measuring the elongation or contraction of sensorsection 25 of one of the torque sensor plates 10 a-10 c. It will beappreciated, however, that the system would also include similarcircuitry operative with transmitter 53 and receiver 54 for sensing theelongation or contraction of sensor section 26 of the respective torquesensor plate, as well as similar circuitry for sensing the contractionand expansion occurring in the other two torque sensor plates during thetransmission of the torque from flywheel disc 2 to clutch disc 4.

Thus, as shown in FIG. 5, the electrical measuring system 50 includes anoscillator 55 for initially driving transmitter 51 via a switch SW untilan acoustical wave from the transmitter is received by the receiver 52.Once such a wave is received by receiver 52, switch SW is opened, sothat the signals received by receiver 52 are thereafter used forcontrolling the frequency of transmission of transmitter 51.

As shown in FIG. 5, the signals received by receiver 52 are fed to acomparator 56 via its input 56 a. Comparator 56 includes a second input56 b connected to a predetermined bias so as to detect a predeterminedfiducial or reference point in the received signal. In the exampleillustrated in FIG. 5, this predetermine fiducial point is the “0”cross-over point of the received signal, and therefore input 56 b is ata zero-bias. Other reference points could be used as the fiducial point,such as the leading edge, the maximum peak, or the minimum peak of thereceived signals.

The output of comparator 56 is fed to an amplifier 57 which is triggeredto produce an output wave or signal for each fiducial point (“0”cross-over point) in the signals received by the receiver 53. Thesignals from amplifier 57 are fed via an OR-gate 58 to the transmitter52. OR-gate 58 also receives the output from oscillator 55 when switchSW is closed.

Switch SW is opened when transmitter 52 receives a continuous stream ofsignals from amplifier 57 via OR-gate 58. When switch SW is opened,transmitter 52 will thus transmit at a frequency determined by thefiducial point in the signals received by the receiver 53 and detectedby comparator 56 to control amplifier 57. Accordingly, the frequency oftransmission by transmitter 52 will be such that the number of waves ofthe cyclically-repeating energy wave transmitted from transmitter 51 andreceived by receiver 52 will be a whole integer.

It will thus be seen that while the frequency of the transmitter 52 willchange with a change in the distance between it and the receiver 53, ascaused by the elongation or contraction of sensor section 25, the numberof wavelengths in the signal transmitted from transmitter 52 will remaina whole integer. This is because, as explained above, the transmitter 52transmissions are controlled by the fiducial points (“0” cross-overpoint) of the signals received by the receiver 53. This change infrequency by the transmitter 52, while maintaining the number of wavesbetween the transmitter and receiver as a whole integer, enables aprecise determination to be made of the distance between the transmitterand receiver. Thus, as known:F=C/λwhere F and C are the frequency and velocity, respectively, of thecyclically-repeating energy wave in the respective medium; and λ is thewavelength.

The “0” cross-over points detected in comparator 56, which are used forcontrolling the frequency of the transmitter 52, are also fed to acounter 60 to be counted “N” times, and the output is fed to anothercounter 61 controlled by a clock 62. Counter 61 produces an output to amicroprocessor 63 which performs the computations of the engine torqueaccording to the elongations and contractions measured, and a display 64which displays the output of the microprocessor.

The output of microprocessor 63 thus represents the measured torque. Itmay be applied as a control signal, as shown at 65, to control the feedof the fuel to the engine or the ignition of the fuel. It may also beused to provide a continuous indication of the engine torque output, theengine condition (e.g., the need for repair or overhaul), or any otherinformation or control relevant to the engine torque output.

Further particulars as to the measuring system illustrated in FIG. 5 areavailable in the above-cited U.S. Pat. No. 6,621,278, the contents ofwhich are incorporated herein by reference. It has been found that usingsuch a measuring system for measuring the above-described deformationsin the torque sensor plate produces a torque measurement of extremelyhigh precision. While such a measuring system is therefore preferred,other electrical measuring systems for measuring the deformations in thetorque sensor plates may be used, such as conventional strain gauges.

It has also been found that using a torque sensor which undergoes anelongation in one section, and a complementary contraction in anothersection, produces not only a highly-precise measurement of torque, butalso a measurement which is relatively insensitive to temperature orangular velocity variations. Thus, the influence of temperature is thesame in both the expansion signal and the contraction signal, andtherefore subtracting one signal from the other eliminates thetemperature influence. In addition, since in the described preferredembodiment, the force which is sensed is a tangential force with respectto the rotary axis, rather than a radial force, the output signalsproduced are relatively unaffected by the rotational velocity, whichproduces radial (centrifugal) forces.

Further advantages of the described torque sensor are that it provides asimple and compact construction which is conveniently incorporatable inexisting vehicle transmission systems and which is capable ofwithstanding harsh environments.

The torque sensor plates are preferably metal in the vehicle embodimentdescribed, producing relatively small elongations and contractions, butin other embodiments, they may be of plastic or elastomeric materialhaving good ultrasound conductivity and producing larger elongations andcontractions. The elongations and contractions of each of the sensorplates 10 a-10 c may be independently measured as described above toproduce a precise measurement of the total torque; alternatively, theelongations and contractions of only one sensor plate may be actuallymeasured and the torque represented by such measurements may bemultiplied by the number of such plates (three) to obtain a closeapproximation of the total torque. The outputs of the sensors may be fedto the electrical measuring system via slip rings, wirelesstransmitters, etc.

FIG. 6 illustrates a modification in the torque sensor plate, thereingenerally designated 110. Torque sensor plate 110 is also made of metaland is formed with the three fastening openings, shown at 111, 112 and113, corresponding to openings 11, 12 and 13 in FIG. 4. In this case,however, each opening is defined by a socket 111 a, 112 a, 113 afloatingly mounted to the remainder of the sensor plate by a circularslot (e.g., 111 b) interrupted by a series of webs 111 c. All the slots111 b, and the corresponding slots formed with respect to openings 112and 113, are filled with an insulating material, preferably an epoxyresin, tending to absorb the acoustical wave reflections produced in thesensor plate.

In the sensor plate 110 illustrated in FIG. 6, the acoustical wavetransmission channels, therein designated 125 and 126 (corresponding tochannels 25 and 26, respectively, in FIG. 4), are also defined by aplurality of slots 141-144, corresponding to slots 41-44, respectively,in FIG. 4. In this case, however, the slots are much wider such as toproduce narrow transmission channels 125, 126, and narrow webs 135, 136,mounting the centerpart of the torque sensor plate to the outerperipheral portion.

As described above with respect to FIG. 4, each of the transmissionchannels 125, 126, includes a transmitter and receiver at its oppositeends, as shown by elements 151-154 corresponding to the transmitters andreceivers 51-54 in FIG. 4.

In all other respects, torque sensor plate 110 illustrated in FIG. 6 isof substantially the same construction, and operates substantially inthe same manner, as torque sensor plate 10 described above with respectto FIGS. 1-5.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art. Forexample, the invention may be implemented in methods and apparatus forsensing or measuring other forces, e.g., weight or the like, and maysense the force applied to other forms of connecting members, such asbolts or the like.

1. A method of measuring a force applied by a first member to a secondmember via a connecting body secured at a first location thereon to saidfirst member, and at a second location thereon, spaced from said firstlocation, to said second member, comprising: transmitting acyclically-repeating acoustical wave through a transmission channel insaid connecting body from a first location thereon to said secondlocation thereon; measuring the transit time of said acoustical wavethrough said transmission channel from said first location to saidsecond location; and utilizing said measured transit time to produce ameasurement of said force; wherein said connecting body is a fasteningplate which fastens said first member to said second member, and saidfirst and second members are a first rotary member and a second rotarymember fastened for rotation together about a common axis of rotation bysaid fastening plate, such that the force measured is the torque appliedby said first rotary member to said second rotary member.
 2. The methodaccording to claim 1, wherein said fastening plate is fixed at a firstfixation point to said first rotary member, and at a second fixationpoint to said second rotary member; said transmission channel of thefastening plate being between said first and second fixation points suchthat said measured transit time of the cyclically-repeating energy waverepresents a measurement of the strain of the fastening plate in saidtransmission channel between said first and second fixation points. 3.The method according to claim 2, wherein said second fixation point isspaced from said first fixation point along a tangential linesubstantially perpendicular to a radial line from said first fixationpoint to said axis of rotation, such that the section of the fasteningplate between said first and second fixation points is deformed by beingexpanded or contracted, depending on the direction of rotation of saidrotary members.
 4. The method according to claim 3, wherein saidfastening plate is also fixed to said second rotary member at a thirdfixation point, said third fixation point being on said tangential linebut on the opposite side of said first fixation point as said secondfixation point, and being equally spaced from said first fixation pointas said second fixation point, such as to produce, between said firstand third fixation points, another transmission channel in the fasteningplate which is deformed in the opposite sense as said first-mentionedtransmission channel during the rotation of said drive shaft; saidlatter deformation also being measured and utilized to produce ameasurement of said torque.
 5. The method according to claim 4, whereinsaid fastening plate is formed with a slot formation defining said firstand second transmission channels in the fastening plate undergoingdeformation during the rotation of the drive shaft.
 6. The methodaccording to claim 1, wherein the two rotary members are coupledtogether by a plurality of said fastening plates equally spacedeccentrically around the axis of rotation of the rotary members.
 7. Themethod according to claim 1, wherein said first rotary member is a driveshaft of a vehicle, and said second rotary member is a driven shaft ofthe vehicle.
 8. A method of measuring a force applied by a first memberto a second member via a connecting body secured at a first locationthereon to said first member, and at a second location thereon, spacedfrom said first location, to said second member, comprising:transmitting a cyclically-repeating acoustical wave through atransmission channel in said connecting body from said first locationthereon to said second location thereon; measuring the transit time ofsaid acoustical wave through said transmission channel from said firstlocation to said second location; and utilizing said measured transittime to produce a measurement of said force; wherein the transit time ofsaid cyclically-repeating acoustical wave from said first location tosaid second location is measured by: detecting a predetermined fiducialpoint in the cyclically-repeating acoustical wave received at saidsecond location; continuously changing the frequency of transmission ofthe cyclically-repeating acoustical wave in accordance with the detectedfiducial point of each received wave such that the number of wavesreceived is a whole integer; and utilizing the measured change infrequency to produce a measurement of said transit time of thecyclically-repeating acoustical wave from said first location to saidsecond location.
 9. Apparatus for measuring a force applied by a firstmember to a second member via a connecting body secured at a firstlocation thereon to said first member, and at a second location thereon,spaced from said first location, to said second member, comprising: atransmitter at a first location on said connecting body for transmittinga cyclically-repeating acoustical wave through a transmission channel insaid connecting body to a second location thereon; a receiver at saidsecond location on said connecting body for receiving saidcyclically-repeating acoustical wave; and an electrical system formeasuring the transit time of the cyclically-repeating acoustical wavethrough said transmission channel from said first location to saidsecond location and for utilizing said measured transit time to producea measurement of said force; wherein said connecting body is a fasteningplate which fastens said first member to said second member, and saidfirst and second members are a first rotary member and a second rotarymember fastened for rotation together about a common axis of rotation bysaid fastening plate, such that the force measured is the torque appliedby said first rotary member to said second rotary member.
 10. Theapparatus according to claim 9, wherein said fastening plate is fixed ata first fixation point to said first rotary member, and at a secondfixation point to said second rotary member; said transmission channelof the fastening plate being between said first and second fixationpoints such that said measured transit time of the cyclically-repeatingenergy wave represents a measurement of the strain of the fasteningplate in said transmission channel between said first and secondfixation points.
 11. The apparatus according to claim 10, wherein saidsecond fixation point is spaced from said first fixation point along atangential line substantially perpendicular to a radial line from saidfirst fixation point to said axis of rotation, such that the deformedsection of the fastening plate between said first and second fixationpoints is expanded or contracted, depending on the direction of rotationof said rotary members.
 12. The apparatus according to claim 11, whereinsaid fastening plate is also fixed to said second rotary member at athird fixation point, said third fixation point being on said tangentialline but on the opposite side of said first fixation point as saidsecond fixation point, and being equally spaced from said first fixationpoint as said second fixation point, such as to produce, between saidfirst and third fixation points, another transmission channel in thefastening plate which is deformed in the opposite sense as saidfirst-mentioned transmission channel during the rotation of said driveshaft; said latter deformation also being measured and utilized toproduce a measurement of said torque.
 13. The apparatus according toclaim 12, wherein said fastening plate is formed with a slot formationdefining said first and second transmission channels in the fasteningplate undergoing deformation during the rotation of the drive shaft.